What is the use of javascript arrays

In JavaScript, an array is a collection of ordered data, used to store large amounts of data. Multiple data can be stored at one time, and the length of the array can be dynamically adjusted; by using arrays, it can be Shorten and simplify program code to a large extent, thereby improving application efficiency.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

JavaScript Array is a collection of ordered data. Each member in the array is called an element, and the name (key) of each element is called the array index (Index). The length of the array is flexible and readable and writable; that is, the length of the array can be dynamically adjusted.

The role of arrays:Storing a large amount of data, multiple data can be stored at one time. By using arrays, program code can be shortened and simplified to a great extent, thereby increasing the efficiency of the application.

In JavaScript, you can use the Array object to define an array. In addition, the Array object also provides various properties and methods related to arrays.

Definition of array: Array Abbreviation: arr

Array is a data container in JS. It is one of the reference types.

Its function is very simple, it is used to hold multiple data, andThe length of the array can be dynamically adjusted.

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How to create array:

• ##Literal

• Constructor

Literal syntax:

var array name = [member 1, member 2, member 3, ...];

Array elements are separated by commas;

Constructor syntax:

var array name = new Array(member 1, member 2, member 3, ...) (at least there must be two or more array elements;)Small bug: when the parameterWhen there is only one parameter and the type of the parameter is a number, it will be regarded as the length of the array;

var arr = new Arry(5 ); console.log(arr); The output result is:

var array name = new Array();

var arr = new Array ();//Create a new empty array

Note that Array 0, A must be capitalized

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The array consists of two parts:

1: Index (also called subscript),

The subscript starts from 0;

2. Members (array elements):

Members have no restrictions and can be any type of data;It can be a string, it can be a number, it can be a Boolean value, it can be undefined, it can be null, it can also be an array;

##Get array elements:

The value of the array:

Array name [subscript]; The subscript starts from zero;

/ / Format: Array name [subscript] Subscript is also called index

/

/ Function: Get the value corresponding to the subscript of the array. If the subscript does not exist, undefined is returned.var arr = ['red',, 'green', 'blue'];

console.log(

arr[0]
); // redconsole.log(arr[2]
) ; // blueaconsole.log(arr[3]
); // The maximum subscript of this array is 2. There is no such array element, so the output result is undefined ;

Add members/modify members through index:

---

// 构造函数定义一个数组 var arr = new Array('张三', '李四', '王五', '赵六') // 添加成员 arr[4] = '龚七' console.log(arr) //张三', '李四', '王五', '赵六','龚七' // 修改成员 arr[0] = '王老五' console.log(arr) //'王老五', '李四', '王五', '赵六'

Special case: Setting multiple members through index will cause interruption in the middle On, empty; prohibited!

var arr = ["a", "b"];

arr[5] = "good";

console.log (arr); //

---

遍历数组:

---

数组的属性length,就是数组成员的个数;

数组名.length

var arr = [1, 2, 3, 4, 5, 6, 7, 8];

length表示数组的长度 它会跟着数组实时发生变化(动态监测数组元素的个数)

console.log(arr.length) //数组成员的个数: 8

length属性可读可写 它也会影响数组的成员个数 但是我们一般不会主动修改该属性;

var arr = [1, 2, 3, 4, 5, 6, 7, 8];

arr.length = 3;

console.log(arr.length);

console.log(arr);

---

数组元素求和,求平均值:

求数组元素的最大值:

数组元素转字符串,并分割开:推荐: 数组名.join("连接符")

求数组中大于10的成员,并挑选出来:

数组元素的倒叙:

---

数组元素的增删改查;

unshift 头增数组名.unshift("value")

作用：头部增加(可以增加多个)

参数:添加的成员,可以是多个;

返回值：数组的新长度

var arr = ['张三', '李四', '王五', '赵六']; var result = arr.unshift('王二',刘一) console.log(result); // 6 console.log(arr); // ["王二", "刘一","张三", "李四", "王五", "赵六"]

push 尾增数组名.push("value")

作用：尾部增加(可以增加多个)

参数:添加的成员,可以是多个;

返回值：数组的新长度

var arr = ['张三', '李四', '王五', '赵六']; var result = arr.push('王二',"刘一") console.log(result); // 6 console.log(arr); // ["张三", "李四", "王五", "赵六", "王二","刘一"]

shift 头删数组名.shift()只删除第一个,()括号内为空;

作用：删除数组的头部第一项

参数:无;

返回值：被删除的那一项

var arr = ['张三', '李四', '王五', '赵六']; var result = arr.shift() console.log(result); // 张三 console.log(arr) // ['李四', '王五', '赵六'];

pop 尾删数组名.pop()只删除最后一个,()括号内为空;

作用：删除数组最后一项;

参数:无;

返回值：被删除的那一项

var arr = ['张三', '李四', '王五', '赵六']; var result = arr.pop(); console.log(result); // 赵六 console.log(arr) //["张三", "李四", "王五"]

concat 拼接,合并;数组名.concat("value")

作用：合并

参数：任意个、任意类型

返回值：一个新的合并后的数组

特点：没有改变原来的数组

var arr1 = [1, 2, 3];

var arr2 = [4, 5, 6];

var newArr =arr1.concat(arr2, "good", true, 1);

console.log(arr1); // 1,2,3

console.log(arr2); //4,5,6

console.log(newArr); //1, 2, 3, 4, 5, 6, "good", true, 1

slice 截取数组名.slice(start,end) 参数是下标; 包括开头,不包括结尾;

slice的本质是复制(浅复制)

作用：截取

参数：

1. 没有参数 截取全部

2. 一个参数 从指定位置截取到最后(包括最后)

3. 两个参数 从指定开始位置截取到指定的结束位置1. 这两个参数都是下标 2. 开始位置(包含) 3. 结束位置(不包含) 4. 第二个参数要比第一个大;

4. 参数可以是负数,负数是从后面开始,最后一个是-1;

特点：不改变原数组

没有参数 (截取全部的)
var arr = ['张三', '李四', '王五', '赵六'];
var arr1 = arr.slice();
console.log(arr1) // ["张三", "李四", "王五", "赵六"]

一个参数 (从指定位置截取到最后(包括最后))
var arr = ['张三', '李四', '王五', '赵六'];
var arr2 = arr.slice(1);
console.log(arr2) // ["李四", "王五", "赵六"]

两个参数 (包括开始,不包括结尾)
var arr = ['张三', '李四', '王五', '赵六'];
var arr3 = arr.slice(1, 3);
console.log(arr3) // ["李四", "王五"]

参数为负数; (还是第二个参数要比第一个大)

var arr = ['张三', '李四', '王五', '赵六','刘一'];
var arr3 = arr.slice(-3, -1);
console.log(arr3) // ["王五","赵六"]

PS: 如果参数是负数 那么表示从后往前数 最后一个值是-1

splice 操作数组 数组名.splice(参数1,参数2,参数3)

作用：用于操作数组成员

参数：

• 参数1:操作开始位置; (从第几个索引号后开始, 可以看成直接从顺序的第几个后开始的)
• 参数2:删除的成员个数;(为0,是添加)
• 参数3:从第三个参数开始是添加的成员;

返回值：被删除的那些成员组成的数组

特点：会改变原数组

// 删除 var arr = ['张三', '李四', '王五', '赵六']; var result = arr.splice(1, 2) console.log(result); // ["李四", "王五"] console.log(arr); // ["张三", "赵六"] ---------------------------------------------------------------------- // 插入 第二个参数为0; var arr = ['张三', '李四', '王五', '赵六']; var result = arr.splice(2, 0, '小绵羊'); console.log(result); // [] console.log(arr) // ["张三", "李四", "小绵羊", "王五", "赵六"] ------------------------------------------------------------------------ // 替换 第一个参数从哪里开始, 第二个参数删除几个,第三个参数...添加的新成员; var arr =['张三', '李四', '王五', '赵六']; var result = arr.splice(2, 1, '小绵羊', '大绵羊'); console.log(result); // ["王五"] console.log(arr) // ["张三", "李四", "小绵羊", "大绵羊","赵六"]

-----------------------------------------------------------------------------------------------

如果只有一个参数 则第二个参数默认为删除所有;

var arr = ['张三', '李四', '王五', '赵六'];

var result = arr.splice(2);

console.log(result); // ["王五","赵六"]

console.log(arr) // ["张三", "李四"]

indexOf 数组名.indexOf("数组元素")

作用： 查找

参数：被查找的成员;

返回值：下标(索引); 若有该成员返回该索引; 若没有就返回-1

var arr = ["a", "b", "c", "d", "e", "f"];

var idx = arr.indexOf("d"); //3

var idx = arr.indexOf("aa"); //-1

console.log(idx);

join 数组名.join("连接符")

作用：转字符串

返回值：数组元素变成字符串类型,链接符相连;

参数： 拼接符号(可选)

数组名.join() 不写内容,默认是逗号, ;

数组名.join(''), '' 没有空格隔开, 数组直接相连;

数组名.join(' ') 空格隔开, 空格

数组名.join('*')

var arr =['张三', '李四', '王五', '赵六']; var str = arr.join(); console.log(str); // 张三,李四,王五,赵六 var str1 = arr.join('+'); console.log(str1); // 张三+李四+王五+赵六 var str2 = arr.join('❤'); console.log(str2); // 张三❤李四❤王五❤赵六

//返回值是数组元素变成字符串,并连接符相连;

reverse 数组倒叙 数组名.reverse() 括号内不跟参数;

作用：将数组的成员倒序

返回值：倒叙的原数组

参数：无

特点：会改变原数组

var arr =['张三', '李四', '王五', '赵六']; console.log(arr) // ["张三", "李四", "王五", "赵六"] var arr1 = arr.reverse(); console.log(arr1) // ["赵六", "王五", "李四", "张三"] console.log(arr === arr1) // true

console.log(arr) // ["赵六", "王五", "李四", "张三"] //会改变原数组;

其他方法:

sort 排序 数组名.sort(函数) 升序或降序

作用：将数组成员按照指定规则排序

返回值：排序后原数组

参数：规则函数; 不跟参数(//不跟参数,会先转为字符串,然后按照ascii码排序首字母排;)

特点：会改变原数组

var arr = [89, 96, 45, 66, 78, 3, 100, 1];

arr.sort(function(a, b) {

return a - b;// 升序

});

console.log(arr); // [1, 3, 45, 66, 78, 89, 96, 100];

-------------------------------------------------------------------------

var arr = [89, 96, 45, 66, 78, 3, 100, 1];

arr.sort(function(a, b) {

return b - a;// 降序

});

console.log(arr); // [100, 96, 89, 78, 66, 45, 3, 1];

--------------------------------------------------------------

var arr = [89, 96, 45, 66, 78, 3, 100, 1];

arr.sort(); //不跟参数,会先转为字符串,然后按照ascii码排序首字母排;

console.log(arr); //[1, 100, 3, 45, 66, 78, 89, 96]

交换两个变量的值

var a = 4; var b = 5; // 交换两个变量的值要借助第三个变量 var c = b; b = a; a = c; console.log(a); // 5 console.log(b); // 4

---

数组的冒泡排序

for (var j = 0; j
for (var i = 0; i
if (arr[i] > arr[i + 1]) {
var temp = arr[i];
arr[i] = arr[i + 1];
arr[i + 1] = temp;
}
}
}

----------------------------------------------------------

要排序 就要比较大小

First compare the first number with the second number. If the first number is larger, swap positions. After the comparison, the number in the second position of the array must be larger than the first one.

Then take the first number After comparing the second and third numbers, the third number in the array must be larger than the number in the second position.

And so on, after one round of comparison, the final number must be the largest

The second round continues the comparison from the beginning. After the second round, the second largest number can be determined

The third round...

to the end.

// // The outer loop determines the execution of the inner loop Number of times

for (var j = 0; j

(var i = 0; i

// Determine if the front is larger and the back is smaller, then exchange

if (arr[i ] > arr[i 1]) {

var temp = arr[i];

arr[i] = arr[i 1];

arr[i 1]=temp;

##Two-dimensional array

Each member of an array is also an array, which is called a two-dimensional array.

---

One-dimensional array: [1, 2, 3, 4, 5, 6]

Two-dimensional array:

[

[1, 2 , 3, 4, 5, 6],

[1, 2, 3, 4, 5, 6],

[1, 2, 3, 4, 5, 6]

...

]

Method to clear the array:

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// Method 1 recommendedarr = [ ];

// Method 2arr.length = 0;
// Method 3
arr.splice(0, arr.length);[Recommended learning:
javascript advanced tutorial
]

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